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2025-10 Cumulative Update for Windows 11 Version 24H2 for x64-based Systems (KB5066835) (26100.6899) will not download and install

MartinB 25 Reputation points
2025-10-15T15:37:45.34+00:00

The update just sits at Downloading - 0%

2025-10 Cumulative Update for Windows 11 Version 24H2 for x64-based Systems (KB5066835) (26100.6899)

After starting downloading, reaching about 27 % it fails - see error message below User's image

Windows for home | Windows 11 | Windows update

4 answers

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  1. Mathias Kainrath 5 Reputation points
    2025-10-17T00:14:39.59+00:00

    Encountering the same issue on my Dell Windows 11 Pro last night, I first did disc check etc. and it did not work. After reading on another webpage that a user was able to fix the problem, by doing a disc clean and cleaning system files, I did the same and after a restart the update successfully installed. In System Cleanup, I cleaned 'Windows Update Cleanup", "Downloaded Program Files", and Temporary Files, restarted and the update finally installed successfully. I hope this helps some of you.

    1 person found this answer helpful.
  2. Krislyn Ong 5 Reputation points
    2025-10-20T01:23:01.2633333+00:00

    I face screen flickering problem after this update. Any idea what happen?

    1 person found this answer helpful.
  3. John Carl Nazario 5,665 Reputation points Independent Advisor
    2025-10-15T16:15:12.75+00:00

    Hi MartinB, thanks for sharing the details. The error code 0x800f0991 usually indicates a problem with Windows Update components or corrupted system files. First, try running the Windows Update Troubleshooter by going to Settings, then System, then Troubleshoot, and selecting Other troubleshooters. Run the Windows Update troubleshooter and apply any fixes it suggests. Second, reset the Windows Update components manually by opening Command Prompt as Administrator and stopping the update services, renaming the SoftwareDistribution and Catroot2 folders, and then restarting the services. After that, restart your PC and try the update again. If the issue persists, you can download and install KB5066835 manually from the Microsoft Update Catalog at https://www.catalog.update.microsoft.com. Finally, if none of these steps work, run DISM and SFC to repair system files using the commands DISM /Online /Cleanup-Image /RestoreHealth and sfc /scannow in an elevated Command Prompt.

    If you found the response helpful feel free to mark my answer as helpful/accepted, it might make it easier for others to find the solution too.

    Best,
    Carl

  4. Diego Nuñez 1 Reputation point
    2025-10-31T18:46:17.4+00:00

    I have the same exact problem. I see some users provide some solutions by doing a disk clean, but I cannot wrap my head around on how to do it unless you guys provide a quick list of explicit easy to follow steps please.

    Otherwise, Microsoft are you listening? this update just keeps on a vicious cycle, downloading-installing-failing at some point and then automatically doing this again and again for over two weeks now.

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